In recent years, small-size imaging devices such as digital still cameras and digital video cameras have widely been spread as home imaging devices. Further improvement in convenience, in particular further size reduction, has been demanded for these small-size imaging devices. To meet the demand, attempts have been made to reduce size and thickness of optical elements installed in the small-size imaging devices. In these days, use of folded optical systems in the small-sized imaging devices has been proposed.
For example, Patent Literature 1 discloses an imaging device including a folded optical system. The imaging device includes an optical system having 5 lens groups. A first lens group which is the closest to the subject constitutes the folded optical system. Specifically, the first lens group consists of a first lens, a prism and a second lens. Light incident on the imaging device is bent substantially vertically by the prism and then enters the second lens. The optical system in the thus-configured imaging device is reduced in thickness because the lens moves in the direction of an optical axis of the second lens for the zooming.
[Patent Literature 1] Published Japanese Patent Application No. 2004-354869